1. Field of the Invention
The present invention relates to a method for determining the type of digital versatile discs (DVD). More particularly, the present invention relates to a method of distinguishing between a DVD− and a DVD+ disc.
2. Description of the Related Art
Digital versatile disc (DVD) is now a very popular optical storage medium. Aside from the read-only DVD-ROM (the “ROM” part refers to a read-only memory), DVD that can be used for recording data is available. DVD that can be used for recording data can be further classified into DVD− and DVD+ according to specifications. At present most DVD players are compatible to a number of specifications. Therefore, the technique of determining the type of a DVD is quite important.
At present, the method of determining the type of a DVD includes using the positional information embedded within a pre-groove wobble signal (wobble signal in short). According to DVD standard specifications, a DVD-ROM does not have a wobble signal. However, both the DVD− and the DVD+ have wobble signals beside ordinary tracks. The source of the wobble signal can be seen with reference to FIG. 1. When the optical disc rotates inside a DVD player, the pick up head 101 will slide away from the track 102 in an outward direction. The relative positions of the four areas A, B, C, D in the photo diode IC (the photosensitive diode integrated circuit) of the pick-up head 101 are set up as shown in FIG. 1. Hence, each area will receive a signal of different magnitudes. The wobble signal is obtained using the following formula:Gx[g1×(A+D)−g2×(B+C)],where G, g1 and g2 are adjustable gain values.
DVD− and DVD+ each has a positioning scheme mixed within the wobble signal that permits the extraction of positional information by decoding using a logic computational circuit. FIG. 2 shows the wobble signal of a DVD+. The wobble signal 201 includes a plurality of phase-changing regions 202. After decoding the wobble signal 201 in a logic computational circuit, positional information is obtained. FIG. 3 shows the wobble signal of a DVD−. The wobble signal 301 includes a plurality of land pre-pits 302. Similarly, positional information can be gathered after the wobble signal is decoded in a logic computational circuit. As shown in FIGS. 2 and 3, DVD+ and DVD− produce different wobble signals and the decoding function of each logic computational circuit is different. Thus, these differences can be utilized to determine the type of a DVD.
FIG. 4 is a flowchart showing the steps of the prior art method for determining the type of a DVD. First, assuming an optical disc placed inside the DVD player is a DVD+ so that parameters related to DVD+ are set up (step 402). An attempt is made to read data about the current position information (step 404). If the current position information is read successful, the optical disc is determined to be a DVD+ (step 406). Otherwise, the optical disc is assumed to be a DVD− and parameters related to a DVD− are set up (step 408). Thereafter, another attempt is made to read data about the current position information (step 410). If the current position information is read successful, the optical disc is determined to be a DVD− (step 412). Otherwise, the optical disc is determined to be a DVD-ROM (step 414).
One major drawback of the aforementioned method is that the related parameters of the DVD+ and the DVD− must encompass most types of optical discs. For an optical disc that has been used to record data before, the quality of positional information on the disc may deteriorate and lead to errors. Hence, a method capable of reducing errors in distinguishing between a DVD+ and a DVD− is required.